1. Field of the Invention:
The present invention relates to an inference method in an inference machine employing a set of knowledge such as rules. More particularly, it relates to an inference method and system well suited for the settlement of a problem in which rules from a plurality of standpoints are applied so as to find different solutions depending upon the standpoints.
2. Description of the Prior Art:
As stated in, for example, the bulletin "Information Processing" of the Information Processing Society of Japan, Vol. 26, No. 12 (1985), pp. 1487-1496, a prior-art inference machine is constructed of a rule set portion which stores a set of rules, an inference portion which interprets and executes the rule, and a working memory which stores the initial state and intermediate state of an inference. The inference portion infers while repeating a finding process which finds the rule executable in the current initial or intermediate state stored in the working memory, a conflict resolution process which finds the optimum rule as the rule to-be-executed in the presence of a plurality of executable rules, and an execution process which executes the rule to-be-executed thereby to compute the next intermediate state and to rewrite the working memory.
In the finding process, the plurality of executable rules are found in such cases:
(1) where a plurality of solutions are possible to a problem, so the rules corresponding to respective alternatives are executable, PA1 (2) where the rule set is redundant, and there are a plurality of lines of inference leading to an identical solution, so the rules corresponding to the respective lines are executable, and PA1 (3) where the rules to be executed in other intermediate states similar to the current intermediate state are executable in the current state.
The conflict resolution process finds the rule to-be-executed on the basis of a resolution method which is designated according to each of the aforecited cases. In the first-mentioned case, namely, the case where the plurality of executable rules have been found in correspondence with the plurality of possible solutions, a priority level method using rule ranks as stated below is employed.
The priority level method sets the precedence degrees of the rules within the rule set before or midway of the inference. By way of example, the method sets the precedence degrees according to which, among rules a, b, c, d and e, the rules a and d have the highest precedence degree, the rules b and c have the second-highest precedence degree, and the rule e has the lowest precedence degree. These items of information shall be called "priority level information." The conflict resolution process selects the rule of the highest precedence degree among the executable rules on the basis of the priority level information.
The priority level method is intended to find the optimum one of the plurality of possible solutions by appropriately setting the priority level information items. With the prior-art inference method, it has been possible to set the priority level information items in only one series.
According to the prior-art technique, the same optimum solution is found for an identical problem at all times.
In the fields of scientific and technical computations, etc., the single optimum solution has existed for one problem. However, in the field of decision making in daily life or business to which the inference machine is directed, there are problem settlements from various standpoints, and the optimum solutions of the individual standpoints can exist for one problem. By way of example, the problem of the plan of shopping involves the standpoint of saving, the standpoint of hoarding, the standpoint of lightening baggage, etc., which have the optimum solutions, respectively.
The inference machine which is truly useful for a user is an inference machine which finds the optimum solution from the user's standpoint, or an inference machine which finds the plurality of optimum solutions of various standpoints, thereby permitting the user to extensively study a problem on the basis of these solutions. As stated before, however, the conventional inference method in the prior art has been capable of finding only one optimum solution.